Apparatus for measuring an analyte concentration from an ocular fluid

ABSTRACT

The present invention relates to a hand-held fluorescence photometer and method for measuring an analyte level, preferably a blood glucose level, from an ocular fluid. The photometer is based on a dual beams measuring system and it is capable of defining the correct positioning for the measurement. Only when the apparatus is correctly positioned the actual analyte measurement automatically takes place.

This application is a national stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/EP2004/0013677 filed Feb. 13, 2004,which claims benefits under 35 U.S.C. 119(a)-(d) or 365(b) of EuropeanPatent Application No. 03003381.5 filed Feb. 14, 2003.

The present invention relates to a hand-held fluorescence photometer andmethods for measuring an analyte level, preferably a blood glucoselevel, from an ocular fluid. The photometer is capable of self definingthe correct position with respect to the eye for measuring. As theapparatus is properly positioned the analyte measurement automaticallytakes place.

One important aspect in the treatment of diabetes is the tight controlof blood glucose levels, which requires frequent monitoring of bloodglucose levels of patients so as to manage food intake and the dosageand timing of insulin injection. Currently, millions of diabetics areforced to draw blood daily to determine their blood sugar levels. Toalleviate the constant discomfort and inconvenience of theseindividuals, substantial effort has been expanded in the search for anon-invasive or minimally invasive technology to accurately determineblood glucose levels.

Various non-invasive or minimally invasive technologies to measure bloodglucose levels from an ocular fluid such as tears, aqueous humor, orinterstitial fluid have been described. Relevant to the presentinvention is the ocular sensor for glucose disclosed in WO-A-01/13783.The ocular sensor described by WO-A-01/13783 is an ophthalmic lenscomprising a glucose receptor labeled with a first fluorescent label anda glucose competitor labeled with a second fluorescent label. The twofluorescent labels are selected in a way that while the competitor isbound to the receptor, the fluorescence of the second fluorescent labelis quenched via a fluorescence resonance energy transfer. By monitoringthe change of the fluorescence intensity at a wavelength around the peakof the fluorescence of the quenchable fluorescent label, the amount ofthe fluorescently labeled competitor that is displaced from the receptorby glucose is measured and provides a means of determining the glucoseconcentration in an ocular fluid. This measurement can, in turn, bemanipulated to provide a measurement of blood glucose level.

Advantageously, the first fluorescent label could serve as an internalstandard in the determination of glucose concentration in an ocularfluid and thereby could enhance the accuracy of determination of glucoseconcentration in an ocular fluid.

WO-A-02/087429 discloses a fluorescence photometer for measuring bloodglucose level from an ocular fluid which is capable of measuringsimultaneously two fluorescence intensities at two different wavelengthsand that could therefore benefit from the measurement system disclosedin WO-A-01/13783.

However the problem of this technology is its high price and complexityfor positioning the measurement tool with respect to the eye of thepatient. The positioning of the measurement beam must be done with anaccuracy of a few micrometers. While this is perhaps possible with astatic measuring system, this is so far impossible with respect to an invivo measurement assembly with an hand-held apparatus. Therefore thereis the need to develop an apparatus for measuring glucose concentrationin ocular fluids which is also capable of self defining the correctposition for measuring, with an accuracy of a few micrometers. Moreoverthe measurement on the eye surface with a hand-held fluorescencephotometer requires a concept ensuring that only the fluorescence of theocular fluid or the contact lens but not the background fluorescence ofthe underlying tissue is measured.

The term “ocular analyte concentration” or “ocular analyte level” asused herein refers to an analyte concentration in an ocular fluid.

The term “blood analyte concentration or level” or “ocular analytelevel” as used herein refers to an analyte concentration in the bloodstream of a person.

The present invention, in one aspect, provides a hand-held fluorescencephotometer for measuring an analyte level, preferably a blood glucoselevel from an ocular fluid based on a dual beam measuring system havingpreferably confocal optical paths.

The fluorescence photometer of the invention comprises:

-   (a) at least a first irradiating means for providing a pilot beam    when in use, wherein said pilot beam is irradiated onto the eye of a    user from outside the cornea of the eye to excite the pupil    fluorescence or first fluorescence wherein said pupil fluorescence    travels along a first optical path;-   (b) a first detecting means located on the first optical path for    detecting the intensity of the pupil fluorescence within the given    wavelength range;-   (c) a second irradiating means for providing a measurement beam when    in use, wherein said measurement beam is irradiated onto the eye of    a user from outside the cornea of the eye to excite an ocular    analyte sensor, wherein said ocular analyte sensor is in contact    with an ocular fluid and upon irradiation with said irradiating    means emits a total fluorescence having at least a second    fluorescence wavelength band, wherein said second fluorescence    travels along a second optical path;-   (d) a second detecting means located on the second optical path for    detecting the intensity of the second fluorescence at the given    wavelength;-   wherein, when the fluorescence photometer is in use, said pilot beam    is positioned at a fixed angle and distance from the measurement    beam, and said angle being greater than 0 degrees and smaller than    90 degrees.

The proper positioning of the apparatus is achieved by measuring thepupil fluorescence intensity, also addressed as first fluorescenceintensity, by means of the pilot beam optical path. The intensity of thepupil fluorescence is in fact correlated to the distance of themeasurement tool from the eye.

Only when the distance of the measurement tool from the eye is such thatthe measurement beam irradiates the iris, the actual measurement starts.The iris has an auto fluorescence which is about 100 times lower thanthe fluorescence of the pupil. Therefore in order to achieve a highsignal/noise ratio it is advantageous to direct the measurement beam tohit the iris of the patient's eye. Whenever the photometer is misplacedthe measurement beam automatically stops.

The small dimensions together with the high accuracy achieved by thephotometer of the present invention allows for the first time to focustwo beams at the same time in a patient's eye and therefore to benefitfrom a dual beam measurement system.

The photometer further includes a calculating means or a processingcircuit for determining based on the measured fluorescence intensities:

-   (a) a distance between the photometer and the patient's eye;-   (b) an ocular analyte concentration in the ocular fluid of the user    according to a predetermined calibration table or calibration curve;    and an arithmetic means for converting the ocular analyte    concentration determined by the calculating means into a blood    analyte concentration by referring to a predetermined correlation    between blood analyte concentrations and ocular analyte    concentrations.

In another aspect, this invention provides a method for measuring ananalyte level, preferably blood glucose level from an ocular fluid. Sucha method comprises:

-   (a) providing an ocular analyte sensor in contact with the tear    fluid;-   (b) providing a hand-held fluorescence photometer in front of the    patient's eye, wherein in use said photometer provides a pilot beam    and a measurement beam;-   (c) irradiating a pilot beam onto the eye of a user from outside the    cornea of the eye to excite the pupil fluorescence or first    fluorescence wherein said first fluorescence travels along a first    optical path;-   (d) detecting the intensity of the first fluorescence within the    given wavelength range;-   (e) correlating the intensity of the pupil fluorescence to the    distance of the fluorescence photometer to the eye and thereby    determining the exact position of the fluorescence photometer for    the measurement; once the exact position has been reached-   (f) irradiating a measurement beam onto the eye of a user from    outside the cornea of the eye to excite the ocular analyte sensor,    wherein said ocular analyte sensor emits a total fluorescence having    at least a second fluorescence wavelength band upon irradiation with    said irradiating means;-   (g) detecting the intensity of the second fluorescence at the given    wavelength;-   (h) correlating said intensity of the second fluorescence to the    analyte level.

In a preferred embodiment the geometry of said fluorescence photometeris such that when the fluorescence photometer is in use, the pilot beamis positioned to a fixed angle and distance from the measurement beamwherein said angle is greater than 0 degrees and smaller than 90degrees; and the measurement beam is irradiated onto the iris of thepatient's eye.

FIGURES

FIG. 1 shows the basic principle of the measurement system according tothe present invention.

FIG. 2 shows the schematic arrangement of the positioning of themeasurement beam and of the pilot beam with respect to a patient's eye;

FIG. 3 shows the optical path of the pilot beam in a preferredembodiment of the present invention;

FIG. 4 shows the optical path of the measurement beam in a preferredembodiment of the present invention;

FIG. 5 illustrates the combined optical path of the measurement beam andof the pilot beam with respect to a patient's eye in a particularembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The basic principle of the measurement system of the present inventionis shown in FIG. 1. First, a pilot beam 1 having a well definedwavelength number irradiates the pupil 2 of a patient's eye 3 wearing anocular analyte sensor (not shown). Such irradiation causes the pupil 2to emit a first fluorescence 11 of a defined wavelength range whichtravels along a first optical path and is measured by means of adetector. The measured fluorescence intensity range is then correlatedto the distance between the fluorescence photometer and the eye.

The geometry of the present fluorescence photometer is such that thepilot beam 1 and a measurement 5 beam which is used for the actualanalyte measurement are positioned to a fixed angle α with respect tothe patient's eye 3 as shown in FIG. 2. When the distance of thephotometer from the eye is such that according to the present geometrythe measurement beam irradiates the iris 6 of the patient, an internalcircuit (not shown) sends a signal to start the actual analytemeasurement. Only then, the measurement beam 5 irradiates the iris 6 ofthe patient's eye 3. Upon irradiation, the ocular analyte sensor emits atotal fluorescence 55 having at least a second wavelength band whichtravels along a second optical path and is measured by means of adetector. The measured fluorescence intensity is then correlated to theanalyte concentration in the blood of the patient.

The angle α is chosen in such a way that the measurement beam irradiatesthe surface eye in the iris 6 with the limits set by the pupil 2 and thesclera depending on the optics of the photometer and on the optimaldistance of measurement. The angle α is greater than 0 degrees andsmaller than 90 degrees. Preferably, the angle α is between 20 and 50degrees and more preferably is between 30 and 40 degrees. A preferredmeasurement distance is between 100 mm and 1 mm, more preferably isbetween 5 and 30 mm.

The pilot beam 1 also causes the emission of fluorescence of the ocularsensor but such a fluorescence can be neglected compared to thefluorescence emitted by the pupil 2. Analogously, the measurement beam 5causes the iris 6 to emit a fluorescence however such a fluorescence maybe neglected compared to the fluorescence generated by the ocularglucose sensor.

Advantageously when the pilot beam irradiates the pupil 2 of thepatient's eye 3, the pupil itself 2 becomes smaller making themeasurement system independent from the pupil 2 versus iris 6 dimensionswhich may vary from patient to patient and on illumination conditions.

FIG. 3 describes schematically the optical path with respect to the eyeof the pilot beam 1 (also shown in FIG. 5) in the fluorescencephotometer of a preferred embodiment. Such a fluorescence photometercomprises a first light emitting diode 7 serving as irradiating means,dichroic mirrors 8, 9 with the dual function of reflecting and splittingthe beam, filters 10, 12 and a first detecting means 13.

The first light emitting diode 7 emits excitation light of a definedwavelength range which travels trough filter 10 to obtain amonochromatic beam or pilot beam. Dichroic mirror 8 directs themeasurement beam towards the patient's eye 3. Before hitting the pupil 2of the patient's eye 3 the pilot beam 1 is collimated and properlyfocused by means of standard lenses (not shown). Such irradiation in theeye 3 causes the pupil 2 to emit a characteristic fluorescence alsoreferred as first fluorescence which travels back to the dichroic mirror8. Then, the dichroic mirror 8 blocks the reflected excitation light andallows the pupil fluorescence, which has a higher wavelength band toproceed further on its optical path. The dichroic mirror 9 directs thepupil fluorescence to filter 12 which makes sure that only the pupilfluorescence having a well defined wavelength range reaches the detector13 and is measured.

FIG. 4 shows schematically the optical path with respect to thepatient's eye 3 of the measurement beam 5 in the fluorescence photometerin a preferred embodiment of the present invention. In this particularembodiment an ocular glucose sensor which emits a total fluorescencehaving a second fluorescence and a third fluorescence at well definedwavelength numbers is used.

The apparatus comprises at least a second light emitting diode 17serving as irradiating means, dichroic mirrors 18, 19 with the dualfunction of reflecting and splitting the beam, a simple mirror 20,filters 21, 22, 23, a second and a third detecting means 24, 25. Thesecond light emitting diode 17 emits excitation light of a definedwavelength range which travels trough filter 21 to obtain amonochromatic beam or measurement beam 5. The dichroic mirror 18 directsthe measurement beam 5 towards the patient's eye 3. Before hitting theiris 6 of the patient's eye 3 the measurement beam 5 is collimated andproperly focused by means of standard lenses (not shown). Suchirradiation of the iris 6 causes the glucose ocular sensor to emit atotal fluorescence which travels back to the dichroic mirror 18. Then,the dichroic mirror 18 blocks the reflected excitation light and allowsthe total fluorescence which has higher wavelength bands to proceedfurther on its optical path. The dichroic mirror 19 splits the totalfluorescence into a second fluorescence having a second wavelength bandand a third fluorescence having a third wavelength band. The secondfluorescence which has a lower wavelength band is then deviated tofilter 22 and the third fluorescence is allowed to pass trough. Filter22 allows only the second fluorescence with a well defined wavelengthnumber to reach the second detector 24.

The third fluorescence band on its optical path encounters mirror 20which directs it to the third detector 25 after being filtered out. Thethird fluorescence having a well defined wavelength number is thenmeasured.

In a particularly preferred embodiment the measurement beam optical pathcomprises more than one light source. An example of this preferredembodiment is illustrated in FIG. 5 wherein the measurement beam opticalpath further comprises a third light emitting diode 27, an additionaldichroic mirror 28 and an additional filter 29. The excitation lightcoming from the second light emitting diode 17 is used to exciteespecially the second fluorescence of the ocular sensor and the thirdlight emitting diode 27 is used to excite especially the thirdfluorescence of the ocular sensor. In the same manner of the dichroicmirrors described earlier, dichroic mirror 28 blocks lower wavelengthnumber and allows the higher wavelength number band to continue in theoptical path.

In a further preferred embodiment the photometer of the presentinvention further comprises one or more additional irradiating means forproviding the pilot beam. The light sources then are preferably used insequence during the positioning of the apparatus and the measurement.

FIG. 5 also shows a possible combination of the preferred optical pathof the pilot beam 1 and of the measurement beam 5 in the fluorescencephotometer of the present invention.

The photometer preferably further includes a calculating means or aprocessing circuit (not shown) for determining based on the measuredfluorescence intensities:

-   (a) a distance between the photometer and the patient's eye;-   (b) an ocular glucose concentration in the ocular fluid of the user    according to a predetermined calibration table or calibration curve;    and an arithmetic means for converting the ocular glucose    concentration determined by the calculating means into a blood    glucose concentration by referring to a predetermined correlation    between blood glucose concentrations and ocular glucose    concentrations. The present invention, in a further aspect, provides    kits for calibrating an apparatus for measuring ocular glucose    concentrations;    and a light-emitting display panel serving as means for displays the    blood glucose concentrations.

To a person skilled in the art it will appear obvious to modify theapparatus described above in the case in which the ocular sensor emits afluorescence with only one wavelength band or in the case in which theocular sensor emits a fluorescence with more than two wavelength bands.For example, the number of dichroic mirrors in the measurement beamoptical path may be diminished or increased. Analogously the number oflight source may be on convenience increased.

The analyte to be measured may be glucose as well as any other substancepresent in an ocular fluid such as hormones. The fluorescence photometerthen has to be modified accordingly within the concept of the invention.For example, both the dichroic mirror and filter positions with respectto the measurement and/or pilot beam optical path have to be optimizeddepending on the ocular analyte sensor and on the optics employed.

The light sources are preferably Surface Mounted Device light emittingdiodes having a defined wavelength range which are characterized byuniform light distribution and smaller power compared to standard lightemitting diodes. In alternative, any other kind of light emittingdiodes, lasers or electroluminescence light sources could be employed.

Dichroic mirrors block lower wavelength number and allow the higherwavelength number band to continue in the optical path. Theirpositioning with respect to the beams optical path as well as the filterpositioning as to be optimized for every specific case measurementsystem.

In a preferred embodiment wherein the ocular glucose sensor emits asecond fluorescence at 520 nm and a third fluorescence at 590 nm, asurface mounted light emitting diode having an excitation light of 465nm is used. The dichroic mirrors and the filters preferably have anangle of 45 and 90 degree respectively with respect to the pilot beamand measurement beam optical paths. The angle α between the pilot beamand the measurement beam in this preferred embodiment is 35 degrees.

The photometer to make these measurements could take severalconfigurations such as a moderate sized laboratory instrument or a smallhand-held, portable, self contained unit suitable for the user to carryeasily in a pocket or purse. For example, the length of the fluorescencephotometer is preferably between 3 and 20 cm, preferably between 5 and15 cm and most preferably between 7 and 10 cm. The thickness is, forexample, between 1 and 7 cm, preferably, between 2 and 4 cm. Theinstrument is used by looking into an optical window while holding theapparatus in front of the eye to a distance which is determined by thepilot beam 1 when the instrument is in use. Preferably an integral coveris provided to protect the optical elements. A display preferably usingliquid crystals or light emitting diodes, which provides readout of theanalyte value and instrument diagnostic including battery status isposition in the internal surface of such a cover 31. In alternative thedisplay is positioned on an external cover. A battery compartment isprovided at the opposite end of the instrument.

To cope with the small dimensions of the photometer the pilot beam aswell as measurement beam preferably have confocal optics. To accuratelyposition the photometer with respect to the patient's eye it isadvantageous that the pilot beam has a sharp focus. To diminish theeffect of eye movement during the glucose measurement the measurementbeam preferably has a more diffuse focus.

An initial calibration process may be required for instance to accountfor differences in natural fluorescence of patients and for the specificcharacteristics of the ocular analyte sensor employed.

In addition, a standardization may be done measuring the fluorescenceintensity of a reference dye, which may have been embedded in the ocularanalyte sensor, wherein such a dye is non-active with respect to theanalyte.

Whenever the ocular sensor comprises more than one fluorescent label,one could serve as an internal standard in the determination of theanalyte concentration in an ocular fluid. An additional calibration maybe done by measuring one fluorescent label while exiting another one.This would compensate for the variation (if any) in intensity of thepilot beam when the distance from the eye is slightly varied (order ofmicrometers).

A calibration table or calibration curve as used herein means a table orcurve containing in correlated form fluorescence intensity orfluorescence intensity ratios and their corresponding actual analyteconcentrations.

If the analyte is glucose, a calibration table or calibration curve canfor instance be obtained once a day or just before testing of bloodglucose levels by using at least three standard solutions with knownglucose concentrations over a glucose concentration range from 30 to 500mg/L. The obtained calibration table or curve is preferably stored inthe apparatus which is used subsequently to determine blood glucoseconcentration.

The correlation between blood glucose concentration and ocular glucoseconcentration can be determined by methods well known in the art. See,for example, March et al., Diabetes Care 5, 259-65, 1982. It ispreferred to store such correlation between blood glucose concentrationand ocular glucose concentration in the apparatus of the presentinvention so that the measurement of ocular glucose concentration can beconverted into a value of blood glucose concentration.

Standard solutions can be provided to a user in calibration kits. Theyare stored in containers, preferably in a rectangular container having aplurality of separate compartments. The kits can also includecalibration instruction.

Further, the measured blood glucose concentration value may betransmitted to another piece of equipment via wire or cable, orwirelessly, such as via radio frequency or infrared transmission. Atelemetry signal can be transmitted to an infusion pump, which canprovide insulin to maintain suitable levels of glucose in the body. Thetelemetry signal may be analog or digital.

Infusion pumps are well known in the art for delivering a selectedmedication to a patient including humans and other animals in accordancewith an administration schedule which can be pre-selected or, in someinstances, preprogrammed. Pumps for use in this invention can be wornexternally or can be directly implanted into the body of a mammal,including a human, to deliver a specific insulin to the mammal incontrolled doses over an extended period of time. Such pumps are wellknown and are described, for example, in U.S. Pat. Nos. 5,957,890,4,923,375, 4,573,994, and 3,731,681.

In another aspect, this invention provides a method for measuring ananalyte level, preferably a blood glucose level from an ocular fluid.First, an ocular analyte sensor in contact with the ocular fluid isprovided; second, providing the fluorescence photometer of the presentinvention. The photometer is used by looking into an optical windowwhile holding the apparatus in front of the eye.

In order to exactly positioning the apparatus the pilot beam isirradiated into the pupil of the patient's eye and the pupilfluorescence is measured. Once the photometer is exactly positioned themeasurement beam is irradiated onto the patient's eye, preferably ontothe iris to excite the ocular analyte sensor. Upon irradiation saidocular analyte sensor emits a fluorescence having at least onewavelength band. The detected fluorescence intensity emitted by thesensor is then correlated to the analyte ocular and/or bloodconcentration.

A suitable ocular sensor is for example an ophthalmic lens comprising ananalyte receptor labeled with a first fluorescent label and an analytecompetitor labeled with a second fluorescent label. The two fluorescentlabels are selected in a way that while the competitor is bound to thereceptor, the fluorescence of one of two fluorescent labels is quenchedvia a fluorescence resonance energy transfer by the other fluorescentlabel. By monitoring the change of the fluorescence intensity at awavelength around the peak of the fluorescence of the quenchablefluorescent label, the amount of the fluorescently labeled competitorthat is displaced from the receptor by the analyte is measured andprovides a means of determining the analyte concentration in an ocularfluid.

Fluorescent labels, such as fluorescein, indocyanine green, malachitegreen, and rhodamine, which are quenched when the competitor moiety isbound but are unquenched when the competitor moiety is not bound, arepreferred for use as quenchable fluorescent label in the ocular glucosesensor. A particularly preferred combination of fluorescent labels isthe combination of fluorescein (donor) and rhodamine (acceptor).

The sensitivity of the ocular glucose sensor can be controlled byaltering the concentration of the quenchable fluorescent label.Increasing the concentration of the quenchable fluorescent label in theocular glucose sensor increases the range of fluorescence intensity andthereby increases the sensitivity of resulting measurements.

The glucose receptor moiety comprises one or more binding site forglucose. The binding site also binds a moiety that competes with glucosefor binding and is therefore referred to herein as a “glucose/competitormoiety binding site”. Binding of both the competitor moiety and glucoseto the glucose/competitor moiety binding site is reversible. Thereceptor moiety can be, for example, antibodies, boronic acid, agenetically engineered bacterial fluoriprotein, or preferablyconcanavalin A (Mansouri & Schultz, Bio/Tech 2:385 (1984)).

It is well known to a person skilled in the art to select a competitormoiety which will compete with glucose for binding to aglucose/competitor moiety binding site. For example, suitablecompetitors to glucose for binding to concanavalin A are a polymericcarbohydrate, in particular dextran, or a glycoconjugate as described inU.S. Pat. No. 5,342,789.

A particular preferred receptor competitor system is a system of alabeled concanavalin A and a labeled dextran, especiallyrhodamine-concanavalin A and fluorescein dextran.

In alternative a suitable ocular analyte sensor may be an ophthalmiclens comprising a protein sensing molecule capable of binding analyteand having the property upon irradiation of emitting a fluorescencelight having at least a fluorescence band that changes in intensity ordecay time in a concentration-dependent manner when said molecule isbound to the analyte. If the analyte is glucose, preferably the proteinis an E. Coli glucose binding protein GGBP or functionally equivalentfragments thereof. Proteins other then GGBP may be used, for example,hexokinase, glucokinase, or mutants of hexokinase or mutants of GGBP.For example, it is especially useful to modify the GGBP molecule toinclude cysteine residues as described in U.S. Pat. No. 6,197,534. Inaddition the sensing molecule may be labeled with one or more detectablelabels like solvent sensitive probes such as dansyl probes,anilinonapthalene probes, deproxyl probes and similar probes which aresensitive to the polarity of the local environment. Other useful probesinclude donor-acceptor pairs such us fluorescein to rhodamine, coumarinto fluorescein or rhodamine. Still another class of useful label pairsinclude fluorophore-quencher pairs such as acrylamide groups, iodine andbromate etc in which the second group is a quencher which decreases thefluorescence intensity of the fluorescent group.

A suitable ocular analyte sensor may in addition comprise a referencedye, e.g. for standardization or calibration purposes, which uponirradiation emits a characteristic fluorescence, wherein such a dye isnon-active with respct to the analyte.

An ophthalmic lens is, for example, a removable lens, such as a contactlens, or a permanently implanted lens, such as an intraocular lens, asubconjunctival lens, or an intracorneal lens. Permanently implantedlenses are particularly well-suited for use in individuals who havecompromised ocular function (e.g., cataracts) and also diabetic disease.

Ophthalmic lenses can be corrective lenses or can be constructed so thatthey do not affect visual acuity. Contact lenses optionally can comprisea tint and are preferably disposable, which reduces the risk ofinfection for the user. As used herein, the term “ophthalmic lens” mayalso refer to a shunt or implant that may rest in the subconjunctivalpart of the eye.

Ophthalmic lenses according to embodiments of the invention can be wornchronically to provide repeated measurements or can be worn for a singlemeasurement. Both qualitative and quantitative measurements can beperformed.

1. A hand-held fluorescence photometer for measuring an analyte levelfrom an ocular fluid comprising: (a) at least a first irradiating meansfor providing a pilot beam when in use, wherein said pilot beam isirradiated onto an eye of a user from outside the cornea of the eye toexcite a pupil fluorescence or first fluorescence wherein said pupilfluorescence travels along a first optical path; (b) a first detectingmeans located on the first optical path for detecting the intensity ofthe pupil fluorescence within a given wavelength range; (c) a secondirradiating means for providing a measurement beam when in use, whereinsaid measurement beam is irradiated onto the eye of a user from outsidethe cornea of the eye to excite an ocular analyte sensor, wherein saidocular analyte sensor is adapted to be in contact with an ocular fluidand wherein said ocular analyte sensor, upon irradiation with saidsecond irradiating means, is adapted to emit a total fluorescence havingat least a second fluorescence wavelength band, wherein said secondfluorescence travels along a second optical path; (d) a second detectingmeans located on the second optical path for detecting the intensity ofthe second fluorescence at a given wavelength; wherein, when thefluorescence photometer is in use, said pilot beam is positioned at afixed angle and distance from the measurement beam wherein said angle isgreater than 0 degrees and smaller than 90 degrees; and (e) acorrelation means for correlating the intensity of the pupilfluorescence to the distance of the fluorescence photometer to the eyeand thereby determining an exact position of the fluorescence photometerfor a measurement, and only providing said measurement once the exactposition has been reached.
 2. The fluorescence photometer of claim 1wherein the fluorescence photometer is adapted to irradiate themeasurement beam onto the iris of the user's eye.
 3. The fluorescencephotometer of claim 1 wherein the pilot beam as well as the measurementbeam have confocal optical paths.
 4. The fluorescence photometer ofclaim 1 wherein the analyte is blood glucose.
 5. The fluorescencephotometer of claim 1 wherein, when the fluorescence photometer is inuse, said ocular analyte sensor emits a total fluorescence having secondand third wavelength bands upon irradiation with said irradiating meansand further comprising: (e) an optical path comprising splitting meansfor splitting said total fluorescence having both bands into the secondfluorescence having said second wavelength band and third fluorescencehaving said third wavelength band, wherein said second fluorescencetravels along the second optical path and said third fluorescencetravels along a third optical path; and (f) a third detecting meanslocated in the third optical path for detecting the intensity of thethird fluorescence at a third wavelength.
 6. The fluorescence photometerof claim 1 further comprising a third irradiating means wherein thesecond irradiating means is used to excite the second fluorescence andthe third irritating means is used to excite a third fluorescence. 7.The fluorescence photometer of claim 1 further comprising a processingcircuit and/or arithmetic means, a display and a power supply.
 8. Amethod to determine an analyte level from an ocular fluid comprising:(a) providing an ocular analyte sensor in contact with the ocular fluid;(b) providing a hand-held fluorescence photometer in front of apatient's eye, wherein in use said photometer provides a pilot beam anda measurement beam; (c) irradiating a pilot beam onto the eye of a userfrom outside the cornea of the eye to excite a pupil fluorescence orfirst fluorescence wherein said first fluorescence travels along a firstoptical path; (d) detecting the intensity of the first fluorescencewithin a given wavelength range; (e) correlating the intensity of thepupil fluorescence to the distance of the fluorescence photometer to theeye and thereby determining an exact position of the fluorescencephotometer for a measurement; and once the exact position has beenreached (f) irradiating a measurement beam onto the eye of a user fromoutside the cornea of the eye to excite the ocular analyte sensor,wherein said ocular analyte sensor emits a total fluorescence having atleast a second fluorescence wavelength band upon irradiation with saidirradiating means; (g) detecting the intensity of the secondfluorescence at a given wavelength; and (h) correlating said intensityof the second fluorescence to the analyte level.
 9. The method of claim8 wherein, when the fluorescence photometer is in use, said pilot beamis positioned at a fixed angle and distance from the measurement beamwherein said angle is greater than 0 degrees and smaller than 90degrees.
 10. The method of claim 8 wherein the measurement beam isirradiated into the iris of the patient's eye.
 11. The method of claim 8wherein the analyte is blood glucose.
 12. The method of claim 8 whereina processing circuit sends a signal to automatically go from step (f) to(g).